1. Field of the Invention
The present invention relates to a circuit board and a manufacturing method therefor and, more particularly, to a circuit board capable of minimizing dielectric loss and distortion in a transmission signal during transmission of high frequency signals or high data transmission, and a manufacturing method therefor.
2. Description of the Related Art
In general, the driving speed of chips such as central processing units (CPUs) used in the communications and computer fields has already approached GHz units. However, circuit boards, on which these chips are mounted and electrically or optically connected to each other, operate at speeds that are significantly lower than the driving speed of chips. The circuit boards have single-layer or multi-layered structures.
Referring to FIG. 1, a conventional circuit board includes a dielectric substrate 1, a grounding surface 3 which is installed on one surface of the dielectric substrate 1 and formed of a conductive metal, and a transmission line 5 which is installed on the other surface of the dielectric substrate 1 and formed of a conductive metal for transmitting signals between components mounted on a chip or the like. The dielectric substrate 1 is formed of a material having significantly high permittivity compared to air, for example, FR4/epoxy, ceramic, or TEFLON(copyright) The transmission line 5 and grounding surface 3 are formed on the dielectric substrate 1 by compression firing or the like. In this case, the electrical characteristics of the transmission line 5 depend on the electrical characteristics of the dielectric substrate 1 besides the material and structure of the transmission line 5. In the circuit board having such a structure, the transmission line 5 directly contacts the dielectric substrate 1, so that a large amount of stray capacitance or dielectric loss is generated.
FIG. 2 is a schematic equivalent circuit diagram of the circuit board of FIG. 1. Referring to FIGS. 1 and 2, the dielectric substrate 1 having a predetermined permittivity xcex5s acts as a capacitor having an electrostatic capacitance Cs. The electrostatic capacitance Cs is referred to as stray capacitance. In this case, as the permittivity xcex5s of the dielectric substrate 1 becomes high, a signal transmitted via a transmission line is considerably bypassed by the bypassing of a high frequency signal and high-speed transmission data. Thus, loss of an electrical signal and distortion of data are caused during transmission of high frequency components and high-speed data transmission. A resistance Rd denotes a virtual loss due to dielectric loss.
Transmission of a high frequency signal is interpreted according to the wave theory. The permittivity xcex5s of the dielectric substrate is divided into a real part permittivity xcex5s1 and an imaginary part permittivity xcex5s2. That is, xcex5s is equal to xcex5s1+jxcex5s2. Also, since a transmission signal is expressed as Aexe2x88x92jkz, k=jxcfx89{square root over (xcexcxcex5s)}, there are terms that are lost by the imaginary part permittivity xcex5s2 of the permittivity xcex5s. Such a loss in a transmission signal is referred to as dielectric loss, which causes loss in an electrical signal of a high frequency component.
Also, in a conventional circuit board, the interference is increased by the influence of a surface wave from the surface of a dielectric substrate in contact with transmission lines.
To solve the above problem, an objective of the present invention is to provide a circuit board in which the effective permittivity between a transmission line and a grounding surface is lowered by isolating at least one part of each of the transmission lines from an upper surface of a dielectric substrate, leading to minimized dielectric loss and distortion in a transmission signal during transmission of a high frequency signal or high-speed data transmission, and a manufacturing method therefor.
The above objective of the present invention is achieved by a circuit board having a dielectric substrate, a grounding surface formed on at least one surface of the dielectric substrate, and transmission lines formed on one surface of the dielectric substrate for transmitting electrical signals, wherein at least a portion of each of the transmission lines is isolated from an upper surface of the dielectric substrate to reduce the effective permittivity between the transmission lines and the grounding surface and reduce dielectric loss.
The above objective of the present invention is also achieved by a circuit board having a dielectric substrate, a grounding surface formed on at least one surface of the dielectric substrate, and transmission lines formed on one surface of the dielectric substrate for transmitting electrical signals, wherein at least a portion of each of the transmission lines is isolated from the upper surface of the dielectric substrate to reduce the effective permittivity between the transmission lines and the grounding surface and reduce dielectric loss, and a cap covers the transmission lines, one end of the cap being grounded to the grounding surface.
The above objective of the present invention is achieved by a method of manufacturing a circuit board, including: forming a sacrificial layer of a predetermined thickness on a dielectric substrate; forming supporter patterns and transmission line patterns by patterning the sacrificial layer, and forming supporters and transmission lines in the supporter patterns and transmission line patterns; removing the sacrificial layer so that the transmission lines are isolated from an upper surface of the dielectric substrate; and forming a grounding surface on at least one surface of the dielectric substrate.
The above objective of the present invention is also achieved by a method of manufacturing a circuit board, including: coating a dielectric substrate with a first polymer to a predetermined height, depositing an adhesive layer and a seed layer on the first polymer, and patterning the seed layer, thereby forming support corresponding regions, pad corresponding regions and ground corresponding regions; coating the patterned seed layer with a second polymer, and patterning and plating the second polymer, thereby forming a metal layer for transmission lines; anisotropically etching exposed portions of the first polymer after removing the second polymer and etching the adhesive layer; and forming supporters by isotropically etching a portion of the first polymer below the metal layer for transmission lines.